Flotation of sulfide ores



United States Patent Ofitice 3,223,238 Patented Dec. 14, 1965 3,223,238 FLQTATION F SULFIDE ORES Norbert M. Bikales, Livingston, N.J., and Robert Ben Booth, Stamford, Conn., assignors to American Cyanamid Company, Stamford, COKIXL, a corporation of Maine No Drawing. Filed Jan. 2, 1963, Ser. No. 248,890 6 Claims. (Cl. 209-166) This invention relates to the beneficiation of sulfide ores for the recovery of mineral values occurring therein. More specifically, it relates to a process of recovering copper and zinc values, wherein a comminuted sulfide ore containing said metals is subjected to froth flotation in the presence of a flotation promoter having the Formula I:

(RO) it n (I) wherein R is an alkyl radical of less than 6 carbons (e.g., methyl, ethyl and amyl); R is hydrogen or methyl; R" is lower alkyl (e.g., methyl, ethyl, propyl, isopropyl, butyl, amyl and hexyl), lower alkenyl (e.g., vinyl and allyl) or aryl (especially monoor bicyclic aryl, e.g., phenyl, tolyl and naphthyl); n is a positive integer less than three.

Appreciable quantities of copper, zinc, lead and iron are recovered from ores which contain these metals as sulfides and are generally termed sulfide ores. Sulfide ores are generally beneficiated by a multi-step process which involves: (1) crushing and then wet-comminuting the ore to obtain an ore pulp, (2) adding a flotation promoter and a frothing agent, and then agitating the ore pulp to produce a froth containing the flotable metal values, and (3) collecting the froth and extracting the values therefrom. This invention provides a new and improved means for accomplishing the purpose of step 2, namely, the promotion of the flotation of the desired minerals.

Prior to this invention, many very satisfactory thiophosphate flotation promoters have been commercially available for beneficiating sulfide ores. Most, if not all, of these operate at their best efiiciency when the pH of the pulp is well above the point of neutrality. In fact, many are commercially useless unless the pH of the pulp is in the range of about 9 to 11. In the treatment of some sulfide ores, this is not a severe problem since the natural pH is near or above neutrality and adjustment of pH to a higher level, if at all necessary, requires addition of only relatively small quantities of basic material (e.g. lime as calcium oxide or hydroxide). Some sulfide ores are more acidic in their natural state, yielding pulps which may have a pH as low as 4 or 5. These, of course, are amenable to flotation treatment with conventional prometers, but require addition of large quantities of basic material to raise the pH to a range of 9-11. When the natural pH is low, and efliciency of the flotation promoter requires a high pH, the cost increases due solely to the required basic material is of notable significance.

Thus, prior to the present invention most flotation promoters for sulfide ores were highly pH sensitive and gave much lower recoveries under neutral and acidic conditions than were obtained if pH conditions were more strongly basic.

It is an object of the present invention to provide a class of flotation promoters for use in beneficiation of sulfide ores for metal values therein.

It is another object to provide a process of recovering copper and zinc values from sulfide ore pulps using a flotation promoter which can operate efficiently at a pH below neutrality, as well as in higher pH ranges.

These and other objects are accomplished in accorda crude sulfide ore material is crushed to about a half inch or smaller, and then ground in an aqueous menstruum to about mesh or smaller. If desired, a pro-crushed, pro-ground ore concentrate may be alternatively employed. The solids content of the aqueous ore suspension or pulp can be adjusted to any desired level, for example, a level in the range of 20% to 35% solids. The pulp can be subjected to the flotation step by admixing it with a compound of Formula I and aerating the resulting mixture in the presence of a frothing agent. The resulting froth containing the copper concentrate is skimmed otf from the flotation cell. This concentrate may be further upgraded, if required, by reflotation. The rejects from the first concentration step are usually discarded, but may be treated by further flotation steps if they contain additional mineral values. The rejects from the second or subsequent upgrading flotation operations may be recycled to extract additional values, if desired.

In the practice of the present invention, conventional flotation machinery can be suitably employed. Likewise, particle size and adjustment of solids content in pulp, flotation procedures, number and length of flotation cycles and after-treatment of flotation concentrates, can be governed by principles well known in the ore extraction art. Conventional frothing agents such as pine oil, cresylic acid, higher alcohols, and polyglycol derivatives may be used, along with conventional modifying agents, if needed.

Concentration of the flotation promoter of Formula I is measured on the basis of, and is adjusted to, the ore content of the pre-fioated pulp. In general, as little as about 0.001 lb./ton yields a useful flotation concentrate. Greater amounts ranging from 0.01 to 0.5 lb./ton of ore result in more complete flotation and are more preferred. The upper limit of promoter usage is governed by a balance of cost of increased usage versus benefit of increased mineral recovery. In terms of practice, this is no higher than 1.0 lb. per ton of ore and is usually considerably less.

If the sulfide ore material contains recoverable zinc values which it is desired to collect, this end is often best accomplished by conditioning the pulp by agitating it with an activating compound. Such compounds are usually,

copper salts and can be used in normal quantities, for example, in the range of about 0.5 to 2.0 lbs./ ton of ore. A frequently used salt is copper sulfate, but this invention contemplates use of others in any amount or, if desired, none at all.

The flotation promoters of the present invention as above stated, are useful over a wide range of pH conditions. It is however, generally desirable to operate at a neutral to slightly basic pH range, although promoters within the scope of this invention are quite eflicient at pH ranges below neutrality, viz: at pHs of about five or higher. If it is desired in the case of a very acidic pulp, lime or an equivalent basic material may be used to raise the pH to the level of neutrality.

It is an advantage of the flotation promoters of this invention that they are highly selective and thus provide a direct means for separating metal constituents in an ore material. For example, if a sulfide ore having copper, zinc and lead values is formed into a pulp as described above, and then subjected to froth flotation in the presence of one of the above promoters, lead is not recovered to any substantial extent in the froth. If the pulp is not preconditioned with a zinc activator, most of the zinc will not be floated, and a froth will thus contain only copper in significant amounts. Alternatively, by preconditioning, the copper and zinc can be floated, leaving the lead in the tailing and yielding a froth uncontaminated thereby.

Among the most suitable promoters Within the scope of Formula I are those wherein each R radical is ethyl or propyl; R is hydrogen, R is allyl, ethyl, isopropyl or n-propyl.

The present invention is more specifically illustrated in the following examples.

EXAMPLE 1 Samples containing 1.25 pounds of a copper ore from the Western United States, containing 0.69% copper, were used for the following flotation experiment.

Portions of crushed sulfide ore were ground for 6 minutes at 60% solids with 1.3 pounds of lime (to raise the pH from 5.8 to 7.4) and 0.05 pound of flotation promoter per ton of ore. The resulting pulp was conditioned for minutes at 22% solids with 0.1 pound of a polypropylene glycol frother (average molecular weight of about 425) and floated for 5 minutes. Tailings from each sample were analyzed for percent copper, higher values being indicative of lower promoter efficiency. Results, using various promoters of the present invention, are reported in the following self-explanatory table.

From the foregoing, it can be seen that the promoters of the present invention are efficient flotation reagents even when flotation is conducted at a pH approximating neutrality.

When samples of the ore treated in Example 1 were floated by the identical procedure except for use of known promoters, allyl amyl xanthate and diethyl thiophosphoryl chloride, in place of those of the present invention, the following results were obtained. It will be noted that the copper losses in the flotation t-ailings are markedly higher than with the promoters listed in Table I.

Table II [Flotation of a copper ore at pH 7.4 using 0.05 lb. of promoter/ton ore] Copper in No. Promoter Tailing (Percent) 1 0511110 CSCHzCH=CHz 0.16

2 (C2H50)2PC1 0.23

4 EXAMPLE 2 The ability of the flotation promoter of the present invention to operate efliciently at a relatively low pH compared with known flotation promoters, is shown by the following experiment.

Samples of 1.25 pounds of a second copper ore from the Western United States were ground for 5 minutes at 60% solids with varying amounts of lime and 0.06 pound of a promoter per ton of ore. The resulting pulp was con ditioned for one minute with 0.09 pound of cresylic acid and 0.025 pound of fuel oil per ton of ore. The ground pulp was floated for 8 minutes; the resulting tailing filtered, dried and then analyzed for residual copper. For comparison, the first run was conducted with a promoter of the present invention without added lime. Similar runs were conducted with two known xanthate promoters at optimum pH for these promoters on ores of this type. The results are shown in the following self-explanatory table.

Table III Lime Copper No. (Lbs/Ton pH Promoter in Tailing Ore) (Percent) ll None 7. 1 (CgH5O)zPS-OH2SC5I'I5- 0.11 3.0 9. 8 Sodium isopropyl xanthate 0.11 3.0 9. 8 Sodium ethyl xanthate 0. 12

From the foregoing, it can be seen that promoters of the present invention give essentially the same recovery without the use of added lime as obtained by prior art promoters, but with the need for about three pounds of lime per ton of ore.

EXAMPLE 3 A sample of a South American ore having 2.2% copper was subjected to the following flotation procedure. Samples of 1.25 pounds of the ore were ground for 8 minutes at 60% solids with 0.1 pound of 0,0-diethyl-S-ethylmercaptomethyl)dithiophosphate per ton of ore. The resulting pulp was conditioned for 2 minutes at 22% solids with 6.0 pounds of sulfuric acid (pH 4.4) per ton of ore, further conditioned for one minute at 22% solids with 0.12 pound of cresylic acid per ton of the pulp and then floated for 7 minutes. The tailing was filtered, dried andanalyzed for residual copper. Analysis showed only 0.3% copper in the tailing.

EXAMPLE 4 A sample of copper ore was floated by the following procedure. A 1.25 pound sample was ground for 6 minutes at 60% solids and then conditioned for 5 minutes with one pound of copper sulfate per ton of ore. 0.1 pound of the promoter used in Example 3 per ton of ore was added and the mixture further conditioned for three minutes. 0.1 pound of pine oil was then added and conditioning was again continued for one additional minute. The pulp was floated for 5 minutes and the concentrate collected. The tailing was filtered, dried and analyzed for residual zinc. Analysis indicated only a trace of zinc in the tailing showing that virtually all zinc had been separated from the gangue.

EXAMPLE 5 The following flotation procedure was conducted on a lead ore from the trist-ate area of the United States. The ore sample, weighing about 1.25 pounds, was ground for 6 minutes at 60% solids with 0.2 pound of sodium cyanide per ton of ore. 0.1 pound of the promoter employed in Example 1 per ton of ore was added and conditioning was continued for an additional two minutes. 0.1 pound of pine oil per ton of ore was added as a frothing reagent and conditioning continued for an additional minute. 2. The process of claim 1 wherein the major metal The conditioned pulp was floated for 4 minutes and the value of the sulfide ore is copper. concentrate collected. Visual observation of the con- 3. The process of claim 1 wherein each R radical is centrate and analysis of the filtered tailing showed no lead ethyl, R is hydrogen, R is ethyl and n is 1. had been floated. 5 4. The process of claim 1 wherein each R radical is We claim: ethyl, R is hydrogen, R" is isopropyl and n is 1.

1. In the process of beneficiating sulfide ores by froth 5. The process of claim 1 wherein each R radical is flotation of an ore pulp in the presence of a chemical ethyl, R is hydrogen, R is n-pr-opyl and n is 1. flotation promoter to recover metal values in said ore, 6. The process of claim 1 wherein each R radical is the improvement wherein the flotation promoter is a 10 ethyl, R is hydrogen, R" is allyl and n is 1.

compound of the formula:

References Cited by the Examiner RE UNITED STATES PATENTS SR 15 1,593,232 7/1926 Whitworth 209-166 (R0) 1,812,839 6/1931 Derby 209-166 wherein each R is an alkyl radical of less than six 2750010 8/1956 Lorenz carbon atoms; R is a member selected from the FOREIGN PATENTS group consisting of hydrogen and methyl; R" is 21 845373 8/1960 Great Britain member selected from the group consisting of lower 20 alkyl, lower alkenyl and carbocyclic aryl of less than HARRY B, THORNTON, Primary Examiner. iiisrseethi-rrnaembered rings; and n 1s a positive lnteger HERBERT L. M ARTIN, Examiner- 

1. IN THE PROCESS OF BENEFICIATING SULFIDE ORES BY FROTH FLOTATION OF AN ORE PULP INTHE PRESENCE OF A CHEMICAL FLOTATION PROMOTER TO RECOVER METAL VALUES IN SAID ORE, THE IMPROVEMENT WHEREIN THE FLOTATION PROMOTER IS A COMPOUND OF THE FORMULA: 